It is necessary to remove field heat and chill produce primarily for the purposes of preserving it during shipment to market. One method of quickly cooling produce is illustrated in U.S. Pat. No. 3,844,132, Produce Cooler and Method of Cooling Product, issued on Oct. 29, 1974. In this patent there is described an apparatus comprising a vacuum chamber for receiving the produce. A vacuum pump is used to reduce the pressure within the chamber to a sub-atmospheric level causing the evaporation of moisture in the produce which acts to take the heat of vaporization from the produce thereby reducing the produce temperature. Water vapor resulting from the vaporization condenses on cooling coils positioned over the produce. The cold water flows down across the produce and further cools it.
Additionally, a recirculation system picks up water from the resevoir at the bottom of the vacuum chamber and sprays it over the produce for a further cooling effect.
To allow removal of the produce from the vacuum chamber after it is cooled, a venting system is provided which permits outside air to flow into the vacuum chamber. Naturally, it is necessary that the chamber be brought to atmospheric pressure before being opened. As shown in this patent, venting is accomplished by opening a valve in a pipe extending from the outside atmosphere into the chamber. The outside air is allowed to flow directly into the chamber to cause the pressure to equalize the atmospheric level.
It is known that one result of the rapid pressure increase within the vacuum chamber is vacuum infiltration of moisture into the product. Such occurs especially with the softer, more pourous products such as lettuce, spinach and the like. This phenomena occurs when water lies on the surface of the produce during rapid pressurization. At this time the surface water is forced into the produce by the pressure internal taking longer to rise than that external the produce. While no permanent harm is done to the produce, the water saturated area remains until evaporation of the water takes place and that can be a time period of twenty-four to forty-eight hours. During this time period the water infiltrated area appears as a bruise or discolored area which is unappealing to a buyer. Obviously with the improvement described in the patent discussed heretofore such water infiltration is more pronounced because of the greater amount of water that is deposited on the produce.
It is therefore the primary object of the subject invention to provide a vacuum cooling apparatus which reduces or substantially eliminates vacuum infiltration of the product.